JQuery roll over two level horizontal menu

This script creates a menu with two levels. The second level is hidden and will only appear when you move over a menu button. The menu buttons of the second level are displayed on a single row. This is a userfriendly menu type and saves a lot of space on the page. Although the second menu slides from under the first menu. This effect is obtained by using JQuery. The menu is built using ul and li tags. The CSS provides the layout.